It is known in the regulation of the fuel/air ratio of internal combustion engines to superimpose a pilot control having a regulation. It is further known that additional correcting quantities can be derived from the behavior of the regulating quantity to compensate for faulty adaptations of the pilot control to modified operating conditions. This compensation is also referred to as adaptation. U.S. Pat. No. 4,584,982 describes, for example, an adaptation with different adaptation quantities in various ranges of the load/speed spectrum of an internal combustion engine. The various adaptation quantities are directed toward compensation for different errors. Three types of errors may be distinguished, according to their cause and effect: errors of a hot film air flow sensor, which have a multiplicative effect on the fuel metering; air leakage influences, which have an additive effect per unit of time; and errors in the compensation of pickup delays of injection valves, which have an additive effect per injection.
Under regulatory requirements, errors pertaining to exhaust gas emissions must be detected by onboard means, optionally with the activation of a malfunction light. Mixture adaptation is also used for fault diagnosis. An error is indicated if, for example, the corrective intervention of the adaptation is too great.
Over the operating life, for the manufacturing tolerance and during unregulated sensor heating, the measured lambda value deviates from the lambda value which is physically present, primarily in the stratified charge mode in engines having direct gasoline injection. Since the mixture adaptation takes the measured lambda into account for error learning, the adaptation in stratified charge mode does not lead to the desired result. For the adaptation, therefore, the operation is switched to homogeneous mode and mixture adaptation is activated.
An engine control program is known from German Patent 198 50 586 which controls switching between stratified charge mode and homogeneous mode.
In stratified charge mode, the engine is operated with a highly stratified cylinder charge and high excess air to obtain the lowest possible fuel consumption. The stratified charge is achieved by delayed fuel injection, which ideally results in a division of the combustion chamber into two zones, with the first zone containing a combustible air-fuel cloud mixture at the spark plug. The first zone is surrounded by the second zone which has an insulating layer composed of air and residual gas. Consumption may be optimized by operating the engine largely unthrottled while avoiding charge exchange losses. The stratified charge mode is preferred at comparatively low load.
At higher load, when optimization of performance is of chief importance, the engine is operated with homogeneous cylinder filling. Homogeneous cylinder filling results from early fuel injection during the intake process. Consequently, there is more time for forming a mixture up to the point of combustion. Performance may be optimized in this mode of operation, for example, by making use of the entire volume of the combustion chamber for filling with the combustible mixture.
Several starting conditions are necessary with regard to adaptation:
For example, the engine temperature must have reached the starting temperature threshold, and the lambda sensor must be ready to operate. In addition, the current values of load and rotational speed must be situated in specific ranges in which learning occurs. This is known from U.S. Pat. No. 4,584,982, for example. Furthermore, the operation must be in homogeneous mode. According to the known program, the mixture adaptation is activated in fixed time intervals.
This may result in a conflict with other control functions, such as the control of tank venting. This control function must be active when the activated carbon filter is under high load. In addition, it is desirable to activate mixture adaptation when the activated carbon filter is under a lesser load and the adaptation is not completely ended.
In light of this background, the object of the present invention is to increase the time period in which the engine is capable of being operated in stratified charge mode with optimal consumption. Switching to homogeneous mode for diagnosis reduces the consumption-related advantages of direct gasoline injection, since homogeneous mode is more unfavorable for consumption than stratified charge mode. Switching to homogeneous mode, which is performed especially for diagnosis, unnecessarily increases the fuel consumption when an error is not present. Switching to homogeneous mode should thus be avoided to the greatest extent possible without compromising the detection of exhaust gas-related errors.
This effect is achieved by the features of claim 1.
In particular, the following steps are carried out for this purpose: for compensating for faulty adaptations of the pilot control of fuel metering for an internal combustion engine which is operated in the at least two different operating modes, homogeneous mode and stratified charge mode,
mixture regulation and adaptation of mixture regulation take place in homogeneous mode
with switching taking place between the operating modes, depending on a desired operating mode which is determined from a plurality of operating mode requirements, each of the operating mode requirements being assigned a priority, and-with the desired operating mode being determined depending on the priorities of the operating mode requirements. The physical priority of the adaptation is elevated in different time references, thus requiring a switch to homogeneous mode.
The requirement of the homogeneous mode for mixture adaptation is thus optimized so that regulatory requirements are satisfied.
A further embodiment provides that the time reference depends on whether an error or suspected error is present.
A further embodiment provides that the engine control program contains, among other elements, a program module which functions as a phase discriminator, a program module which functions as a base adaptation requester GA_requestor, a program module which functions as a base adaptation stop GA_stop, and a program module which functions as an end discriminator.
A further embodiment provides that, for low load on the activated carbon filter, the mixture adaptation requestor (GA_requester) program module requests mixture adaptation (GA) for a time TGAPA of less than one minute if the other starting conditions of the mixture adaptation have been met.
A further embodiment provides that the mixture adaptation stop (GA_stop) program module prohibits the phase discriminator from requesting mixture adaptation when the activated carbon filter has a high fuel load and when mixture adaptation is ended.
A further embodiment provides that the phase discriminator program module elevates the physical priority of the mixture adaptation in different time references, thus requiring a switch to homogeneous mode.
A further embodiment provides that these time references depend on whether an error is known to the control unit or whether a suspected error is present.
The present invention is also based on an electronic control device for carrying out at least one of the described methods and embodiments.
In normal everyday operation of the motor vehicle, switching to homogeneous mode is requested only when mixture adaptation is also able to become active. If no errors are present in the system, the mixture adaptation is activated only within certain time intervals. The time segments in which the motor vehicle may be operated favorably for consumption in stratified charge mode may thus be increased over an average time.